This invention relates to a method and apparatus for linking charging records generated during multi-leg calls in a telecommunication network.
While the invention is particularly directed to the art. of telecommunications, and will be thus described with specific reference thereto, it will be appreciated that the invention may have usefulness in other fields and applications.
By way of background, wireless telecommunication networks, which are well known, allow mobile devices to communicate with each other and other networks, such as the Internet and the Public Switched Telephone Network (PSTN). First and second generation wireless telephone systems are generally constrained in the amount of bandwidth available for communication, which limits capacity and also the types of services that can be provided. Third generation (3G) wireless systems, such as the IP Multimedia Subsystem (IMS) which are being developed through the 3rd Generation Partnership Project (3GPP), hold the promise of greater bandwidth, thereby increasing capacity and allowing for enhanced services, such as multimedia services.
Thus, 3GPP is becoming the new worldwide standard for the creation, delivery, and playback of multimedia over new, high-speed wireless networks. 3GPP enables the free sharing of multimedia files between a variety of devices, including cell phones, personal digital assistants (PDAs), and notebook and desktop computers. 3GPP devices include, in addition to a voice communication interface, capability for communication of data and display of data, including video.
Of course, the systems of multiple network operators may be used to carry a given call and such operators may levy charges for the services they provide in connection with the call. As a result, the IMS network entities involved in a session generally send accounting information to a CCF (Charging Collector Function) located in the same domain. The CCF will collect all this information and build a CDR (Charging Data Record), which is sent to the Billing Domain (BD). Each session carries an ICID (IMS Charging Identifier) as a unique identifier. This helps operators to track the charges for a call. The current standards, however, do not work as well when it comes to charging for multiple call legs on a single call.
The standards allow for certain entities in the IMS under certain circumstances to generate multiple outgoing call legs for a single incoming event. A call leg refers to the one-to-one signaling relationship between two user agents. And a call is a collection of call legs. In the call control specification, additional call legs are created through special mechanisms, as known to those skilled in the art. There are several reasons that multiple call legs may be generated: Redirection to realize call forwarding, Refer to realize call transfer and conferencing, Retry on Error, and Serial and Parallel Forking. The standards indicate that in some cases, all call legs are assigned the same ICID but leave some cases unspecified. As a result, when multiple call legs occur during a call, the charging system will typically receive charging records from the various IMS nodes associated with the different branches of the request, all with the same ICID. There is insufficient information to uniquely identify the records associated with a particular leg or to determine the sequence in which the legs were created. As a result, it is possible that only the final successful call leg will be charged, even when, for example, the final node on a preceding leg causes a redirection to a different user.
By way of example, call processing functionality as defined in 3GPP TS 23.228 and RFC 3261 currently provides for redirection (3GPP TS 23.229 clause 5.11.5 and RFC 3261 section 8.1.3.4), and the charging data is contained in the Accounting Request (ACR) and the Charging Data Record (CDR) (Tables 6.4 to 6.10) as defined in 3GPP TS 32.260 for Offline Charging. The current procedures allow for an IMS entity to handle a redirection response (e.g., “302”) by initiating a subsequent INVITE request to the new destination identified by the contact header in the redirection response with an ICID different from the original call leg.
However, the current IMS specifications for the redirection of calls between IMS entities do not clearly explain how the identification of each successive call leg is stored and correlated to one another. For billing purposes, such correlation is necessary to bill all appropriate parties in a redirected call. The ACRs and CDRs do not include any information related to redirection of calls. Since the redirecting and redirected call legs have separate CDRs with different ICIDs, the network operator's Billing Domain cannot identify the entity that initiated a redirect and cannot associate a redirected call leg with the incoming call. Similar problems may occur with respect to Refer, Retry on Error, and Serial and Parallel Forking.
Accordingly, the present invention contemplates a new and improved method and apparatus that resolves the above-referenced difficulties and others.